Network sharing is a way for operators to share the heavy deployment costs for mobile networks (PLMNs), especially in the roll-out phase. A network sharing architecture allows different core network operators to connect to a shared radio access network (RAN), wherein the operators do not only share the radio network elements, but may also share the radio resources themselves. In addition to this shared RAN, the operators may or may not have additional dedicated RANs, like for example, 2G radio access networks.
In the current economical situation, the RAN sharing features are becoming more and more important in order to share the CAPEX and OPEX costs of 3G roll-out. The existing network sharing architectures allow to share the capital cost of the equipments (typically RNCs, NodeBs, Antennas, SW licenses) as well as the operational cost of the network (Energy consumption, maintenance costs, lub transmission costs if the transmission is shared).
There are two identified main techniques or configurations for RAN sharing architecture which are used today in the 3G networks (see, for instance, “The art of RAN-sharing” by Zhou Lin, “China Mobile the accelerating elephant”, Huawei technologies COMMUNICATE, Issue 35, p.p., 50-52, October 2007):                The Multiple Operator Core Network (MOCN) which is a feature standardized by the 3GPP (3GPP TS 23.251 “Network Sharing; Architecture and functional description; Release 6”). MOCN is a pooled spectrum approach which allows multiple operators to share the spectrum, i.e. to run a network using a single 5 MHz carrier, which can be useful in situation when the spectrum is a scarce resource. The drawback of this configuration is that special effort (SIMs, special signalling) has to be used in order to guarantee that the user terminals can display the correct operator code or Public Land Mobile Network-Identifier (PLMN-Id). Besides, RAN sharing by a MOCN requires the plurality of operators for an agreement on a common set of parameters and feature activation, since the radio resources (UMTS cells) are common for all the operators (there is a single shared carrier=1 sector). In the MOCN configuration, multiple Core Network (CN) nodes are connected to the same RNC and the CN nodes are operated by the different operators.        The RAN Sharing with Dedicated Carrier (RS-DC) is a dedicated spectrum approach, not standardized currently, which uses a Dedicated Carrier (sector of cells) per operator. Every operator handles its own spectrum (i.e., its own UMTS cells) and as a consequence each operator can choose its appropriate set of parameters, with the aim to create a consistent user experience across the whole network (made of multiple separated areas where the sharing is not applied and areas where the sharing is applied).        
Hence, when the spectrum is a scarce resource (e.g. in UMTS900), usage of MOON is preferred. However, when traffic grows, there is a need to increase the number of carriers and RAN Sharing with Dedicated Carrier is preferred.
Particularly, in the network scenario of UMTS900 services, the 900 MHz Spectrum is mainly used by speech services and UMTS technology can be activated in order to increase the system capacity for speech in CS (circuit switching) domain or in order to offer new PS (packet switching) services. A single UMTS Carrier can be created using the 900 MHz spectrum for a plurality of operators in the MOON architecture for RAN sharing. But, if one carrier is loaded, and many CS speech calls are rejected in UMTS or redirected to 2G RANs due to the load, this indicates that a sufficient amount of user terminals are asking for a second carrier.
In addition, the usage of MOON is preferred when the energy cost (OPEX) of radiating one carrier is preferred over radiating two carriers with the RAN Sharing Dedicated Carrier Technique.
Therefore, an automatic technique for switching between both features (the pooled spectrum approach and the dedicated spectrum approach) is needed nowadays to make the change of network configuration easy and dynamical, since a manual switch to configure separately and activate one or another is a difficult task.